The interaction of the amyloid β(1-40) peptide with model membranes

The amyloid beta (1-40) peptide (Abeta) is the main component of amyloid deposits found in the brain of patients afflichted with Alzheimer's disease. After treatment with hexafluoroisopropanol, commercial Abeta is readily soluble in water and buffers at pH 7.4 and has an irregular secondary structure. The adsorption of Abeta to the water-air interface and to the surface of the dipalmitoyl-phosphatidylethanolamine monolayer at a surface pressure pi close to zero leads to an increase in pressure up to 17 mN/m. When being adsorbed, the molecules of the peptide occupy a part of the monolayer surface, which leads to the compression of lipid molecules forming the monolayer. Further compression of the monolayer composed of the molecules of the lipid and peptide leads to the extrusion of the peptide from the monolayer. If the lipid monolayer is preliminarily (prior to the addition of the peptide to the liquid phase) compressed to pi = 30 mN/m, no adsorption of the peptide to the monolayer occurs. No changes in the structure of the dipalmitoyl-phosphatidylethanolamine monolayer were detected by the sliding X-ray diffraction method, indicating the absence of specific interactions. The method of reflection and absorption infrared spectroscopy makes it possible to determine the conformation of the adsorbed peptide and its orientation in the lipid monolayer. It was found that Abeta has the conformation of a beta-fold oriented parallel to the interface, as it is the case with the adsorption of peptide molecules to the lipid monolayer at pi < 30 mN/m and upon adsorption to the interface that is not occupied by the lipid.